MADISON, Wis. (AP) — The FBI is helping to look for a 13-year-old Wisconsin boy who disappeared in June, with investigators giving lie-detector tests to relatives and others, a sheriff’s detective said.

James Yoblonski’s father reported him missing June 12 from the family’s home in Reedsburg, about 45 miles northwest of Madison. About three hours before William Yoblonski reported his son missing, a sheriff’s deputy had found the family’s van abandoned in the nearby town of Sumpter.

James Yoblonski had taken his father’s cellphone, and a ping led sheriff’s deputies to search an area around Devil’s Lake State Park, in the same general area. They found a makeshift campsite they believe the boy used. His devices showed searches earlier this year about how to travel out of state.

Sgt. Drew Bulin, a detective with the Sauk County Sheriff’s Office, told WiscNews on Thursday that the FBI joined the search about two weeks ago. Bureau investigators have been administering lie-detector tests to family members and potential witnesses, Bulin said.

William Yoblonski has offered a $10,000 reward for information that leads to finding his son.

“I just want my son back,” he said Thursday.